Some devices are arranged to increase a temperature of a medium (such as water) above an ambient or normal temperature of the medium and store the medium having the increased temperature. These devices may be referred to as thermal energy storage devices. Some thermal energy storage devices are ubiquitous, such as water heaters, which are utilized in modern housing facilities, commercial establishments and other applications to provide hot water for daily use. While water heaters operate to increase the temperature of water over an ambient temperature of the water, they also store the heated water so the heated water is available for immediate use on demand when needed. These devices receive the medium (e.g., water) in a reservoir, heat the medium, store the medium at an increased temperature, and provide the medium having the increased temperature on demand.
A temperature distribution of a medium in a thermal energy storage device in the form of a water heater typically consists of three regions, hot water in the top region of the reservoir, cold water in a lower region of the reservoir, and a thermocline region between the hot water region and cold water region. The position of the thermocline region corresponds to a boundary of the cold and hot water in the reservoir.
As discussed below, the present disclosure provides apparatus and methods for monitoring and providing information regarding a thermocline region and an energy state of a thermal energy storage device, such as a water heater.